Pressure cooker and similar container



'May 5, 1942. A. VISCHER, JR

PRESSURE COOKER A ND SIMILAR CONTAINER 2 Sheets-Sheet 1 4 Filed Nov. 18,1938' QM QM mm ill/IA 3 WM @QQdMZ May 1942- A. vls cHER, JR

PRESSURE COOKER AND SIMILAR CONTAINER Patented May 5, 1942 PRESSURECOOKER AND SIMILAR CONTAINER Alfred Vischer, Jr., Park Ridge, 111.,assignor to V 2 Vischer Products Company, Chicago, 111., a corporationof Illinois Application November 18, 1938, Serial No. 241,118

31 Claims.

The invention relates generally to-closures for containers, and moreparticularly to improvements in pressure cookers.

Most pressure cookers now on the market are provided with clamps andsealing means of various kinds to hold the cover in place. These clampsmust be very strong since the total force which they must be capable ofwithstanding may be as high as several thousand pounds. The clampingmeans must therefore be of substantial construction, and the containeror pot or the cooker must he of sumcient strength at the point where theclamps are attached to form a suitable anchorage ior the clamps.Furthermore, in pressure cookers provided with cover clamps it isnecessary to make the cover very heavy and strong in orderto prevent itsedge from raising from the kettle between the clamps.

It is an object of the invention to provide an improved form of closurefor pressure cookers and similar containers in which the usual clamps tohold the cover in place are unnecessary.

A further object is to provide an improved circular closure for acontainer, which is larger in diameter than the diameter of the circularopening in the container, and which is normally warped or may be warpedso as to be insertable into the container through the opening.

A further object is to provide an improved closure for pressure cookersand similar containers in which the closure cannot be removed until thepressure in the container drops to substantially atmospheric pressure,thereby to eliminate the dangers of escaping steam, due to prematureopening of the container.

A further object is to provide an improved pressure cooker having aclosure which will be held in place by the pressure within thecontainer, and in which the effectiveness of the seal will increase withincreased pressure within the container.

Other objects will appear irom'the following description, referencebeing had to the accompanying drawings, in which: v

Figure l is a perspective view of the pressure cooker;

' Figure 2 is a central vertical sectional view; Figures 3 and 4 aresectional views taken on the lines 3-3 and 44 of Figure 2;

I Figure 5 is an enlarged fragmentary sectional view showing the sealbetween the cover and the Figure 7 is a view showing the cover in itswarped position, the section being taken in a plane perpendicular tothat of Figure 6;

Figure 8 is a central vertical sectionalview of a modified form of theinvention;

Figure 9 is a transverse sectional view taken on'the line 9-9 of Figure8;

Figure 10 is an enlarged fragmentary sectional view showing the sealbetween the cover and the saucepan; and

Figure ii is a plan view diagrammatically illustrating the position ofthe cover in the saucepan prior to being drawn into sealing relationship with the saucepan.

in the accompanying drawings, the invention is illustrated as applied topressure cookers, it being understood that while the invention is of aparticular utility in this form, it may be utilized in other'kinds ofapparatus.

This application is a continuation in part of my copending applicationSerial No. 108,197, filed October 29, 1936, which application was acontinuation in part of my application Serial No. 723,831, filed lviay4,1934.

The form of the invention shown in Figures 1 to 7 includes a saucepan itshown as a casting, preferably made of aluminum or an aluminum alloy.The saucepan is generally cylindrical in shape, but at its upper end isof reduced diameter to provide a cover guiding surface it, a cylindricalcover centering wall it, and a hori zontal downwardly racing seatingsurface it.

- The surface it is preferably machined or otherwise suitably finishedto make it substantially plane and smooth. The saucepan it is providedwith an integral handle socket boss 22 in which a nut it is cast as aninsert. A hardened, knurled metal ferrule it is pressed into a bore 3tformed in the socket boss 22, and has a handle it, preferably of asuitable heat insulating molded plastic material, fitted therein. Thehandle is preferably hollow and has its outer end closed by a cap 32provided with a metal insert washer it. The handle is secured in thebore tli by a handle rod 36, the inner end of which is threaded in thenut 24 and the outer end of which is provided with an eye 38 forconvenience in hanging the cooker upon a hook.

The closure or cover 40 for the saucepan it, when in operative position,as shown in Figure 2, has a shape corresponding substantially to that ofthe surface of a sphere, and is circular in its projection upon ahorizontal plane. As best shown in Figure 5, the cover 40 has anupwardly directed peripheral flange 42 and is provided with gasket 44which may be made of suitable heat and moisture resistant syntheticrubber substi-. tute which is bonded to the cover 40. The cover has acentral hole 48 formed therein to receive a centrally drilled screw 48which serves as a fas-' tening means for a connection fitting 50. Thefitting 58 is internally threaded to receive the attaching screw 48, andis provided with an annular groove receiving a gasket 52 for sealing thejoint. The attaching screw 48 has a pair of perpendicular diametralkerfs 54 which, in addition to'providing a slot for a driving tool, formducts for the flow of steam into the fitting 50, and thus hinderpossible stoppage of the hole through the screw 48 by particles of food.The connection fitting is preferably a die casting and has the end of acover handle rod 56 cast therein as an insert.

A pivot bracket 58 is likewise preferably a die casting, cast about therod 56 with the latter as an insert. The pivot bracket 58 has adownwardly extending toe portion 50 which projects into a tapped hole 62formed in the socket boss 22, the toe portion 60 resting upon the end ofa screw 64 which is threaded in the tapped hole 62. The cover handle rod56 is provided with a molded plastic handle 66, the outer end of whichis closed by a metallic cap 68 which may be pressed into the end of thehandle 66. A latch '18 is freely pivoted on the cover handle rod 56,being constrained against movement longitudinally of the rod by thepivot bracket 58 and a sleeve III. The latch 18 has a hook portion 12which may engage beneath the ferrule 28. The portion of the hook IIIwhich surrounds the rod 56 has knurling 13 formed thereon so as to makeit possible conveniently to operate the latch hook by means of thethumb. The hook portion I2 of the latch engages the ferrule 28 in .amanner such that as the hook I is swung clockwise (Figure 4), the rod 56will be pulled downwardly closer to the rod 36. The ferrule 28 ispreferably knurled or otherwise serrated so as to prevent the hookportion 12 from slipping with respect the ferrule. The rod 56 isresilient and may be flexed slightly in bringing the latch hook I8intoengagement with the ferrule 28.

The connection fitting 50 has a hollow stem -I4 threaded therein andextending vertically therefrom, the upper end of the stem forming a seatfor a valve I6 formed at the end of a screw I8 which is threaded in aweight 80 and molded as an insert in a heat insulating knob 82. Theweight 88 has a counterbore 84 which is of sufficiently great diameter,with respect to the outer diameter of the stem 14, to provide an annularing flange 42 thereon.

The cover is made by stamping a circular blank from a sheet and formingthe upwardly extend- The cover may then be formed by means of a press toassume the shape substantially of a portion of the surface of a sphere,as illustrated in Figure 2. After this operation, the flange 42 may betrimmed to the proper size, and the cover worked to a shape,

when unconstrained, as shown in Figures 6 and 7. To accomplish thislatter working operation, the cover may be secured at its center to arotating chuck, and have its peripheral edge portion engaged by a pairof non-rotating arms provided with contacting rollers by which pressureis applied at diametrically opposite sides of the convex surface of thecover. By this operation, the cover is progressively warped aboutdiametrical axes until it assumes the warped shape shown in Figures 6and 7 when it is unconstrained by any external forces. When in thelatter shape, the closure approaches somewhat the-shape of a portion ofa cylindrical surface.

Under these circumstances, the vertical projection of the cover issubstantially in the form of an ellipse, indicated bythe line I00 ofFigure 11, while the opening in the saucepan is shown as a circle 88.The vertical projection of the peripheral edge of the cover, asindicated by the line I80 (Figure 11), has a major axis which is greaterin length than the diameter of the opening 88 and a minor axis which isless than the diameter of the opening 98. Because of this, the cover maybe inserted through the opening 98 in the direction of its major axisuntil the leading edge of the cover abuts against the inner wall of thesaucepan I4 directly beneath the guiding surface I6. Thereafter, thecover may be tilted so as to bring its edge completely within thesaucepan I4 beneath the sealing surface 20. Then by raising the centerof the cover, it will be guided by the guiding surface I6 into theposition in which it is shown in Figure 2, with its gasket 44 inengagement with the seating surface 20, as shown in Figures 2 and 5. Toraise the cover to this position, the toe B8 of the bracket 58 isinserted into the hole 62 in abutment with the end of the screw 64, andthe handles 26 and 66 pressed together, thus applypassageway for theescape of steam. A pressure I indicating device 86 having an indicatingpointer 88 cooperating with a notched indicating scale 90, is threadedin the connection fitting 50.

The cover 40 has a hole 92 punched therein to receive a pressure reliefdevice 94 which may be made of a suitable heat, acid, and greaseresistant rubber substitute. The device 94 is in the form of a plughaving flanges 96 engaging opposite sides of the cover 48. The plug hassufllcient resiliency that it will be maintained in the aperture 92unless the pressure within the saucepan I4 exceeds a predeterminedmaximum pressure. It will be seen from the drawings that the cover 40,when in operative position, is circular in shape and that the opening 98formed in the top of the saucepan I4 is likewise circular in shape, butof substantially lesser diameter than I t e outside diameter of thecover 40. The cover ing an upwardly directed force to the center of thecover. The cover is then latched in position by swinging the latch hookI8, I2 clockwise to the position in which it is shown in Figure 4.

When the cover is in the unconstrained shape shown in Figures 6 and '7,the internal stresses are in equilibrium. After insertion of the closurewithin the container, the closure is brought into contact with theseating surface 28 along diametrically opposite portions of itsperipheral edge. Thereafter, the handles 26 and 66 are pressed togetherto raise the central portion of the closure, and the extent to which thediametrically opposite portions of the closure are brought ,into contactwith the seating surface 28 is progressively increased. As the closureis drawn against the seating surface, the force required to bring theedge of the closure into contact with the seating surface becomes lessand less as the closure approaches its symmetrical unwarped shape inwhich the scaling is completed. As a result of applying the diminishingtributor of heat, while the stainless steel portion I I2 is highlyresistant to attack by the acids and I being cooked.

pressure relief valve I6 from the end of the stem The steam pressureagainst the inside of the closure will increase the tightness of theseal at the surface 20 as the pressure increases. a result, asteam-tight seal between the cover and the saucepan is assured at alltimes.

If, through carelessness in. cleaning the cooker, the passageway throughthe stem 14 should become clogged, and thus prevent the operation of thepressure regulating valve 16, a dangerously high pressure mightbe builtup within the saucepan were it not for the provision of the pressurerelief device 94 which acts as a safety plug and is deformed and blownoutwardly whenever the pressure within the saucepan exceeds the normaloperating pressure by a predetermined amount.

In inserting the cover 40 in the saucepan, the guiding surface I and thecentering surface I8 01 the saucepan serve the useful function ofassuring that the cover will be accurately centered beneath the opening98.

In Figure 8, I have shown a modified form of container in which theshell I02 is drawn from stainless sheet steel, the shell having aseating surface I04 for the closure and a centering cylindrical surfaceI06 to assure proper engagement of the peripheral edge of the cover withthe seating surface I04. The upper end of the shell is provided with afinishing and reenforcing bead I08 which aids in strengthening theflange which provides the seating surface I04. A bottom III] is made ofbi-metal consisting of a thin layer I I2 of stainless steel and a thickouter layer II4 of mild steel. The peripheral edge of the bottom has anupwardly directed flange IIIi into which the lower edge of th shell I02telescopes, the shell and bottom being seam-welded together.

The container is provided with a handle socket I II, which may be analuminum die casting having an' insert H8. The insert extends beyond thesocket so as to provide an outwardly extending flange I which'is weldedto the shell I02. Theremaining parts of the cooker are substantiallyidentical with the construction previously described, and similar partshave therefore been designated by similar reference characters.difference between the two constructions resides,

.however, in the fact that in the construction of Figure 8 the gasketmay, if desired, be omitted. Instead, the upwardlydirected peripheralflange I22 of the closure I24 has its upper edge rounded as indicated atI26 (Figure 10), and thus makes substantially a circular line contactwith the seating surface I04. The closure I24 is sulficiently flexiblethat it will conform to slight irregularities in the conformation of theseating surface I04, and since the total force applied by the steampressure to the cover is concentrated along the very limited area ofcontact between the closure and the seating surface I04, the unitpressure at the line of contact is very high. As

a result, the closure will form a steam-tight joint with the seatingsurface I04 ofthe shell.

other chemicals which may be present in the food The mild steel portionI I4 reenforces the layer of stainless steel H2 so that the bottom willbe rigid and withstand the pressure to which it is subjected during use,without appreciable deformation. The outer surface of the bottom ispreferably protected against corrosion by a suitable black finish toafford maximum heat absorption.

A gasket such as the gasket 44 not only serves as a means to facilitatethe making of a pressuretight seal, but also provideselectricalinsulation between the cover and the saucepan to prevent acorrosion of these parts by electrolysis. Since, in the constructionshown in Figure 10, the cover and the container are of the samematerial, it is not essential to provide such electrical insulationbetween the two parts.

In the following claims it will be understood that in specifying theclosure or cover to be in its operative shape" it is intended to referto the shape of the closure as it is shown in Figs. 2 and 8, and, as acorollary, when its warped shape is specified, it is intended to referto the shape in which the closure is shown in Figs. 6, 7, and 11,wherein the vertical projection (i. e., the projection, as seen in Fig.11, on a plane perpendicular to the polar axis of the closure), has anoverall dimension (the minor axis of its generally ellipti- .caloutline) which is sufficiently less than the diameter of the circularopening 00 (Fig. 11)

. same or equivalent means.

I claim; 1. An internal warpable resilient disc-like closure providedabout its periphery with a seat engaging rim designed ,to make seatingcontact with a substantially plane and circular seat, the

III

The use of the bi-metal bottom III) has some I .material advantages inthat the mild steel portion thereof acts as a good conductor anddisinternal condition in the material of the body portion of saiddisc-like closure being such as to bring said closure when not subjectedto external forces, into a warped shape having a major and a minor axis,the said minor axis being less than the diameter of the circular seat.whereby said disc may be passed freely through said circular seat, saiddisc-like closure being provided with means for applying and maintainingan external force thereto outwardly thereof to cause the closure toassume and maintain its operative shape with its peripheral rim inengagement with the aforesaid seat.

2. In a pressure cooker. the combination of a container having acircular opening therein and having an inwardly facing substantiallyplane seating surface surrounding said opening, a warpable resilientsheet metal closure having a circular peripheral edge engaging saidseating surface to form a fluid-tight seal, and means to hold saidclosure against said seating-surface, said closure being internallystressed to cause it to assume a warped shape when free from externalforces, said warped shape being one in which the distance between a pairof diametrically opposite points on the peripheral edge of the closureis appreciably less than the diameter of the opening in said container,whereby said closure when in its warped shape may be freely removed fromand inserted into said container through the opening therein.

3. In a pressure cooker, the combination of a containerhaving a circularopening therein and having an inwardly facing substantially planeseating surface surrounding said opening, and a waipable resilient sheetmetal closure provided with means about its periphery cooperable withsaid seating surface to form a fluid-tight seal, the internal stressesin said closure being such as to cause said closure to assume a warpedshape when free from external forces, said warped shape being one inwhich the distance between a pair of diametrically opposite points onthe periphery of the closure is appreciably less than the diameter ofthe opening in said container, whereby said closure when in its warpedshape may be freely inserted and removed through the opening in saidcontainer.

4. The combination set forth in claim 3 in which manually operable meansare provided for pulling the central portion of said closure out ward ywith respect to said container when the closure is in its warpedcondition with portions of the peripheral edge thereof in engagementwith said seating surface, whereby said application of force will causesaid closure to conform to a shape in which its peripheral edge liessubstan tially in a plane and in engagement with said seating surface.

5. The combination set forth in claim 3 in which a handle is attached tothe central portion of said closure, means are provided for pivoting.said handle with respect to said container, and

including latching means for holding said handle in a predeterminedposition.

6. A closure for containers having circular openings surrounded by planeinwardly directed seating surfaces, comprising a warpable resilientdisc-like sheet of metal provided about its periphery with a seatengaging rim for making sealing contact with the seatlngsurface on thecontainer, the internal conditions inthe material of which the bodyportion of the closure is made being such as to bring said closure, whenfree from external forces, into a warped shape in which the distancebetween two diametrically opposite points on its periphery isappreciably less than the distance between diametrically opposite pointsspaced 90" from the first named points, and is also appreciably lessthan the diameter of the container opening to be closed,

whereby said closure may be passed freely through the opening in thecontainer and by applying an external force to said closure, theinternal conditions which cause warping of the closure maybe overcomeand its peripheral edge may be brought into a plane circular shape ofgreater diameter than that of the opening in the containen '7. Apressure cooker comprising-a, container having a substantially circularopening formed therein and having an annular inwardly facing seatingsurface surrounding said opening, and a resilient sheet metal closuresubstantially circular when in operative shape and of diametermaterially greater than that of said opening. said closure beingsumciently elastic to warp without xceeding its elastic limit to a shapein which the vertical projection of its periphery has a dimensionsubstantially less than the diameter of said opening, and cooperativemeans acting between said container and said closure to maintain saidclosure in its operative shape with its periphery in sealing engagementwith said seating surface.

8. An internal warpable resilient disc-like closure when in itsoperative shape having a periphery cooperable with a plane seatingsurface, said closure being subjected to internal forces which warp itto a shape in which the distance between diametrically opposite pointson its periphery in one direction is considerably less than the distancebetween diametrically opposite points on its periphery in a directionperpendicular to said first direction, the internal forces in saidclosure being such that by application of an external force it mayreadily be deformed to an operative shape in which its peripheral edgelies in a circular plane.

9. In a pressure cooker, the combination of a container having acircular opening therein and having an inwardly directed plane seatingsurface surrounding the opening, a resilient sheet metal closure forsaid opening, said closure being subjected to internal stresses in suchmanner that it may assume a warped shape in which the internal stressesare in equilibrium and may assume an operative shape in which itsperipheral edge is circular in shape and in which the internal stressesare in substantial equilibrium, whereby when said closure is in itswarped shape it may be freely inserted through said opening so as tohave portions of its peripheral edge engage said plane seating surfaceand when sub- Jected to an external force its entire peripheral edgewill engage said seating surface to make sealing contact therewith, andmeans for applying said external force to the central portion of saidclosure.

10. The combination set forth in claim 2 in which said closure has anoutwardly directed flange at its peripheral edge.

'11. The combination set forth in claim 2 in which said closure isdished and surface facing outwardly.

' 12. The combination setv forth in claim 2 in which a gasket isprovided between the peripheral ,edge of said closure and the seatingsurface to seal the connection and to provide electrical insulationbetween the closure and the container.

13. The combination set forth in claim 2 in which the means to hold saidclosure against saidseating surface consists of manually operableslightly resilient means for applying an outwardly directed forcesubstantially centrally of the closure.

14. The combination set forth in claim 2 in which the means for holdingthe peripheral edge of the closure against said seating surfacecomprises a handle having its end secured to said applies an outwardlydirected force to'the closure at substantially the center thereof.

15. The combination set forth in claim 2 in which the means to holdtheperipheral edge of the closure against said seating surface includesa manually operable member, and means to hold said member in positionapplying an outwardly directed force to said closure at substantiallythe center thereof.

16. The combination set forth in claim 2 in has its convex v which saidcontainer is provided with a radially outwardly extending handle, and inwhich the means for holding the peripheral edge portion of the closureagainst said seating surface includes a slightly yieldable handleattached to said closure substantially at the center thereof, extendingin a direction generally parallel to the container handle and providedwith a pivot intermediate its ends cooperable with the container, andmeans are provided to hold said handles in substantially fixed positionwith respect to each other.

1'7. The combination set forth in claim 2 in which a fitting having apassageway extending therethrough is attached to said closure at sub--.stantially the center-thereof, and in which the means for holding theclosure against the seating surface includes means connected to saidfitting for exerting an outwardly directed force upon said closuresuflicient to flex said closure and cause its peripheral edge portion toseat against said seating surface, and a pressure controlling device issecured to said fitting and communi cates with the passagewaytherethrough.

18. In ai pressure cooker, the combination of a container having anopening formed in the top thereof and having an inwardlyfacing flatseating surface surrounding said opening and a centering wall ofgenerally cylindrical shape surrounding said seating surface, and aclosure of flexible sheet metal having its peripheral edge engaging saidseating surface and prevented from moving laterally from said seatingsurface by said centering wall.

19. In combination, a container having a substantially circular openingtherein, a cover adapted to be inserted into said container through saidopening, said cover being normally warped so that its projection on ahorizontal plane is substantially an ellipse, the minor axis of which isless than the diameter of said opening in the container, and meansoperable after the cover has been placed in said container for applyingan outwardly directed force to said cover at approximately the centerthereof, said cover being so conformed that upon application of suchexternal force it will be deformed into a circular shape.

20. A closure for a circular opening in a con 'tainer comprising aflexible resilient dished metallic circular sheet internally stressed soas a container having an inwardly extending annular flange at the topthereof, a closure for the circular opening in said flange, said closurebeing circular when in its operative shape but being normally warped bythe internal stresses therein to a shape enabling its free insertioninto said container through said opening despite the greater diameter ofthe closure, and means to pull the peripheral edge of said closure intosealing contact with the inner surface of said flange.

24. In a pressure cooker, the combination of a generally cylindricalcontainer having a substantially circular opening at its top, saidopening being of diameter less than that of the container directlybeneath the top, said container having an inwardly facing plane seatingsurface around said opening, a dished circular cover formed of thinresilient sheet metal of diameter greater than that of said opening,said cover having a peripheral flange but being internally stressed soas normally to assume a sufliciently warped shape that it may be easilyinserted in said container through said opening, and means to apply anoutwardly directed force to substantially the center of said coverthereby to pull the entire peripheral flange of said cover into sealingcontact with the seating surface of the top of said container.

25. In a pressure cooker, the combination of a generally cylindricalcontainer having a substantially circular opening at its top, saidopening being of diameter less than that of the container. directlybeneath the top, said container having an inwardly facing plane seatingsurface around said opening, a dished circular cover formed of thinelastic sheet metal of diameter greater than that of said opening, saidcover to assume a warped shape when not subjected to external stresses,said closure being sufficiently elastic that it may be forced into itscircular shape without exceeding the elastic limit of the metal of whichit is made.

21. A closure for circular openings in containers comprising a circularsheet of flexible metal of diameter appreciably greater than that of theopening to be closed, said sheet, when in operative position closingsaid opening, having a form defined by substantially parallel surfacesof revolution, and containing internal stresses capable of causing it towarp, when not constrained by external forces, to a shape in which itmay be freely inserted in said opening.

22. In combination, a container having a wall with a circular openingtherein, and a circular sheet metal closure for said opening of greaterdiameter than said opening, said closure being normally held against theinner surface of said wall and when unconstrained being deformed byinternal forces to a shape permitting its free,

removal from the container through said opening. 23. In a pressurecooker, the combination of having a peripheral flange but beinginternally stressed so as normally to assume a sufficiently warped shapethat it may be easily inserted in said container through said opening,and means to apply an outwardly directed force to substantially thecenter of said cover thereby to pull the entire peripheral flange ofsaid cover into sealing contact with the seating surface of the top ofsaid container, said means comprising a pair of handles,'one secured tosaid container and the other secured to said cover, means intermediatethe ends of one of said handles to hold said handles separated, andinterengaging latching means to hold said handles together.

26. In a pressure cooker, the combination of a container having acircular opening surrounded by an internal inwardly facing seatingsurface, a handle secured to said container, a fulcrum associated withsaid handle, a flexible closure for said containerof shape similar tothat of said open ing but having each major dimension greater than thecorresponding dimension of the opening, said cover being capable ofwarping along a diameter thereof to an extent sufficient to permit freeinsertion of said cover into said container, a handle secured to thecenter of said cover and having a part engaging said fulcrum, saidhandle extending generally perpendicular to the diameter of the coveralong which it warps,

and latching means on said handles whereby said closure handle may belatched in position to hold said closure in operative position with itsperipheral edge in engagement with said seating surface.

27. A normally warped elastic flexible sheet metal closure, internallystressed when constrained in dished operative position and which, whenunconstrained, resumes its predetermined 1 said closure is insertableonly when it is in its warped shape, and means for applying a pullingforce to the central portion of said closure while portions of theperiphery thereof are in engagement with the internal surface of thecontainer adjacent its opening, thereby to cause the entire peripheraledge 01' the closure to be drawn into sealing engagement with saidsurface of said container.

30. In a pressure cooker, the combination of a container having acircular opening therein and having an inwardly facing substantiallyplane seating surface surrounding said opening, a

warpable resilient sheet metal closure having a circular peripheral edgeengaging said seating surface to form a fluid-tight seal when in closingposition, and means to apply a force outwardly on said closure to holdit against said seating surface, said closure being internally stressedto cause it to assume a warped substantially elliptical shape when freedfrom external forces and in its inoperative shape, said warped shapebeing one in which the distance between a pair of diametrically oppositepoints on the peripheral edge of the closure is appreciably less thanthe diameter of the opening in said container, whereby said closure whenin its warped shape may be freely removed from and inserted into saidcontainer through the opening therein.

31. A closure for a circular opening in a container comprising aflexible resilient dished metallic circular sheet internally stressed soas to assume a warped shape substantially along a diametral line whennot subjected to external stresses, said closure being sufiicientlyelastic that it may be forced into its circular shape without exceedingthe elastic limit of the metal of which it is made.

ALFRED VISCHER, JR.

